<div id="editor">
	<p>lorem<span> ipsum&nbsp;<strong>dolor sit </strong></span>amet</p>
</div>

<script>
	CKEDITOR.replace( 'editor', {
		extraAllowedContent: 'span',
		extraPlugins: 'spanwidget',
		allowedContent: true
	} );

	CKEDITOR.plugins.add( 'spanwidget', {
		requires: 'widget',
		init: function ( editor )	{
			editor.widgets.add( 'spanwidget', {
				upcast: function ( element ) {
					return element.name == 'span';
				}
			} );
		}
	} );
</script>
